This invention relates generally to electrical signal processing means and more particularly to correlation apparatus and methods utilizing coordinate transformation of the Mellin transform type.
Processing of data via optical means is well known in the art, the primary advantage being that optical processing of large amounts of data is achieved in a highly parallel substantially instantaneous manner. Additionally, coherent optical processors have been proposed to perform many and varied functions, including Fourier transformation analysis of analog signals and the correlation therebetween.
In applicants' prior patents, namely U.S. Pat. Nos. 4,071,907; 4,073,010; 4,084,255; and 4,099,249 there are disclosed among other things methods and apparatus for correlating by optical apparatus two functions which are logarithmic scaled and thereafter Fourier transformed to produce Mellin transforms that are scale and shift invariant. Moreover, such signal processing when carried out in connection with radar signals having Doppler information, this information appears in the location of the correlation peak of the processor output. The patent references referred to above moreover disclose not only means for optically performing signal and dual dimensional Fourier transforms, but also means for optically implementing a holographic matched spatial filter. These patents may be referred to for a more detailed treatment of this type of optical correlator and moreover, are meant to be incorporated by reference in the present specification.